FDA Refuses to Review Moderna’s New Flu Shot

The U.S. Food and Drug Administration (FDA) recently informed Moderna that it would not review the company’s application for approval of its new flu vaccine, which is its first using mRNA technology for influenza.

The FDA has been going back and forth with Moderna for nearly two years since the company submitted Phase 3 data on the vaccine. That data showed the effectiveness of the mRNA flu vaccine, called mRNA 1010.6, when compared to existing flu shots.

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Moderna posted on its website a timeline of its communications with the FDA, in which the agency asked for additional information comparing how Moderna’s flu shot stacked up against existing ones for older people, who are more vulnerable to flu complications. The company says it started a Phase 3 study in 2025 involving more than 40,000 people over age 50—some of whom took mRNA 1010.6, and others who took the flu shot Fluarix.

In the FDA’s letter to Moderna, which the company posted on its website, the agency said the application “is not sufficiently complete to enable a substantive review.” Dr. Vinay Prasad, director of the Center for Biologics Evaluation and Research (CBER) at FDA, signed the letter and faulted the lack of data on a control against which Moderna’s flu vaccine can be compared. “CBER does not consider the application to contain a trial ‘adequate and well-controlled’ and the application is therefore, on its face, inadequate for review. This is because your control arm does not reflect the best-available standard of care in the United States at the time of the study.”

According to reporting by STAT, Prasad made the decision against the advice of staff at FDA, who recommended reviewing the application and were prepared to do so. The decision reflects growing scrutiny and restrictions on vaccines under the Trump Administration; Prasad also overruled FDA staff in limiting yearly COVID vaccines to people over 65 and those with weakened immune systems.

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At issue with Moderna’s mRNA flu shot is communication from CBER to Moderna suggesting that the company’s vaccine be compared against a control shot designed more specifically for older people. Moderna says the FDA didn’t directly request any changes to the design of the study.

FDA spokesperson Andrew Nixon said in a statement, however, that “the FDA rejected Moderna’s application for filing because the company refused to follow very clear FDA guidance from 2024 to test its product in a clinical trial against a CDC-recommended [high-dose] flu vaccine to compare safety and efficacy,” and said “Moderna exposed participants age 65 and over to increased risk of severe illness by giving them a substandard of care against the recommendation of FDA scientists.”

Moderna maintains that the company provided the needed control comparison for older people. “The letter is inconsistent with previous written communications from CBER to Moderna,” the company said in a statement. The company also says “CBER did not raise any objections or clinical hold comments about the adequacy of the Phase 3 trial after the submission of the protocol in April 2024 or at any time before the initiation of the study in September 2024.”

Moderna’s mRNA flu vaccine is being reviewed outside of the U.S.—in Europe, Canada, and Australia—and the company plans to submit requests for approval in other countries as well this year.

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The FDA’s decision could mean that people in other countries would get the first mRNA flu shots before Americans do. One important advantage of the mRNA technology is its speed; currently, the World Health Organization reviews data from flu cases in the southern hemisphere before making a recommendation about which strains seem to be causing the most disease, and recommending those for the next yearly updated flu shot. That generally happens in the spring, ahead of the fall and winter flu season in the northern hemisphere, which includes the U.S. and Europe. About 80% of current flu shots are made by growing the influenza virus in chicken eggs, which requires months of advance planning. Some shots are made with more modern technology, such as cell-based platforms, but the majority are still made using decades-old methods that take time.

mRNA technology, on the other hand, takes just weeks to incorporate new virus strains, as the world saw with the quick development of the COVID vaccines matched to the strains causing the most disease. mRNA based technology could help health officials to respond more quickly to changing varieties of influenza, and ultimately prevent and protect against more disease.

Since taking office in January, the Trump Administration has been dismantling existing policies and recommendations about vaccines. Secretary of Health and Human Services (HHS) Robert F. Kennedy Jr., who oversees the major health agencies including FDA and the U.S. Centers for Disease Control and Prevention (CDC), has removed and replaced members of the CDC’s expert committee that reviews and makes recommendations about which Americans should receive which vaccines. He also removed recommendations for most children and adults to get annual flu and COVID shots. Earlier this year, HHS canceled a $590 million contract with Moderna to develop an mRNA-based bird flu vaccine, before Kennedy said the government’s Biomedical Advanced Research and Development Authority, which was involved in that development, would be “winding down” mRNA vaccine work in favor of other platforms.